Polymer Science, Series B最新文献

In this study, the hydrothermal method was used to synthesize the rare earth catalyst ethylene glycol cerium (EG-Ce), and its catalytical performance on polyethylene glycol terephthalate (PET) and low-melting polyethylene glycol terephthalate (LmPET) were investigated. Using the rare earth catalyst EG-Ce, cerium-catalytic polyester (PET-Ce), and cerium-catalytic low-melting point polyester (LmPET-Ce) were effectively synthesized. The differences in melting point, inherent viscosity, thermal stability, and other parameters of the PET produced by the EG-Ce and traditional ethylene glycol antimony (EG-Sb) were compared. The outcomes demonstrate that the rare earth catalyst EG-Ce had superior catalytic activity than EG‑Sb in the polymerization process. The LmPET produced by EG-Ce also exhibited excellent mechanical properties and adhesive quality than the items which produced by EG-Sb. The rare earth-based catalyst reduced the safety risk than heavy metal antimony, indicating that is a good candidate as a catalyst in polyester and low-melting polyester synthesis.

Solvent-free polyurethane acrylate (PUA) by UV-cured process generally has low molecular weight, and thus shows weak mechanical properties, which limited its application. Herein, five kinds of linear polyetheramine modified polyurethane acrylates (PUPEA) were prepared using polyetheramine (PEA) instead of partial acrylic monomers as capping agents at the end of the polyurethane to improve the resilience and elongation. Structures of PUPEA were characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (¹H NMR). Mechanical properties, hydrophobicity and thermodynamic properties of the obtained PUPEA were investigated and compared with those of conventional PUA. The results show that the semi-capping polyurethane with PEA instead of HEA can significantly improve the resilience and flexibility, specially, the flexibility increases about thrice to fourfold higher than those of PUA. Moreover, PUPEAs provide the self-healing properties and self-adhesive properties, while the conventional PUA does not have. Therefore, the introduction of PEA can effectively regulate the properties of PUA, which expands the application of UV-curable polyurethane elastomers in flexible electronic sensors.

Using the polymerization filling technique, composite materials have been obtained based on ultra-high molecular weight PE and fillers of platelike (graphene or graphite nanoplatelets) and spherical (silica) types. The tensile stress–strain characteristics of samples obtained using different pressing modes have been examined. It has been revealed that the cooling rate of the samples during pressing affects the values of ultimate tensile strength and modulus of elasticity in tension. The characteristics of composites processed at a low cooling rate (10 K/h) are 30% higher than those of the samples obtained at a high cooling rate (10 K/min). Using DSC, DMA, and X-ray diffraction methods, it has been shown that the way of cooling affects the crystallite size of compressed samples of composite materials.

The chemical oxidative polymerization (COP) method was used in the lab to create the nanocomposite materials polypyrrole (PPY), reduced graphene oxide (rGO), polypyrrole-copper oxide (PPY-CuO), and polypyrrole-copper oxide-graphene oxide (PPY-CuO-GO). It was discovered by analysis of the X-Ray diffraction (XRD) results that CuO was successfully absorbed into the surface of PPY with an average crystallite size of 38 nm. The aggregation in the PPY polymer chain was accelerated by the anisotropic behavior of CuO. The conductivity of the PPY-CuO-GO nanocomposite was considerably improved, and the current density was enriched. When compared to the original PPY, the PPY-CuO-rGO nanocomposite was shown to have an improved current density of 49.20 A/cm² and reduced band gap 1.92 eV. The PPY-CuO-rGO nanocomposite can be employed as an electron transporting layer (ETL) material for organic light emitting diodes (OLED) application due to the increased current density and high electron-hole recombination rate.

The operating conditions of products made of polymeric materials significantly affect their service life. Herein we have investigated the influence of duration of natural climatic factors of the Republic of Sakha (Yakutia) (very cold climate zone) impact on the structure and properties of polyethylene grade 273-83. IR spectroscopic studies have shown that radical oxidative reactions causing a decrease in the polymer molecular weight occur in the material during long-term natural exposure. Investigation of the melt flow index has shown that, besides the reactions accompanied by rupture of the macromolecular chains, crosslinking processes also occur in the polymer. These processes lead to a decrease in the polymer molecular weight and broadening of the molecular weight distribution. It has been shown that the change in the degree of crystallinity and the lamellas thickness is non-monotonic and is determined by the weather conditions during the exposure period. Changes in the intensity of solar radiation, as well as average daily and seasonal temperatures of the ambient air, together with chemical changes occurring in the polymer during natural exposure, lead to the appearance of areas of ordered structures in the amorphous phase, resulting in the decrease in thickness of the amorphous phase which determines the material plasticity. Therefore, the stresses in the macromolecular chains of the polymer in the amorphous phase are so much increased that the polymer exhibits the behavior of a brittle material.

Submicron composite particles with the core/shell structure are synthesized by the seeded emulsion polymerization of a mixture of various acrylates in the presence of a redox initiation system. The diameter, morphology, and surface structure of particles as well as their ability to self-assemble into 3D ordered thin-film structures are studied by scanning electron microscopy, FTIR spectroscopy, thermogravimetry, and dynamic light scattering. It is shown that under the used experimental conditions particles with a shell thickness of 10‒35 nm are synthesized. The effect of shell composition (in particular, the alkyl chain length of acrylate comonomers) on the morphology and structure of the surface layer of the obtained composite particles is traced.

Polymerization of 5-vinyltetrazole under conditions of radical initiation in aqueous media in the presence of chitosan gave network graft copolymers, the structure of which is built from chitosan macromolecules crosslinked by chain fragments of poly(5-vinyltetrazole). It was determined that the polymerization is preceded by the formation of a saltlike product between chitosan macromolecules and vinyl monomer, which affects its polymerization activity. The obtained graft copolymers are prone to limited swelling in water to form pH-sensitive ampholytic hydrogels.

Carbon dioxide is a well-known green solvent, and can be used instead of some organic solvent to prepare the polymer products. On the basis of its poor solubility, dispersion polymerization can be adopted to produce the polymer products in industry. Thus, low price, easily available stabilizers with good stabilization effect will be a must. In this paper, we are committed to designing and synthesizing stabilizers with these characteristics. Firstly, thiol ethanol is used as the chain-transfer agent to control the copolymerization of vinyl acetate/vinyl propionate, and the homopolymers or copolymers with the hydroxyl group at the chain terminal are obtained. These homopolymers or copolymers are then functionalized to prepare the stabilizers with methacrylate groups. The results indicate that these stabilizers can effectively control the dispersion polymerization of methyl methacrylate in supercritical carbon dioxide. The proportion of structural units in the copolymer and the concentration of stabilizer or initiator obviously affect the conversion percentage of methyl methacrylate and the molecular weight of polymers. The maximum conversion percentage of methyl methacrylate and the molecular weight of poly(methyl methacrylate) can reach 93%, and 56000 Da, respectively. SEM images show that most of the samples are free-flowing powders with a spherical structure.

Unitary metal hydride reduction systems (diisobutyl aluminum hydride and lithium aluminum hydride) and binary metal hydride reduction systems (sodium borohydride/diisobutyl aluminum hydride and lithium aluminum hydride/diisobutyl aluminum hydride) were used to reduce liquid terminated-carboxyl fluoroelastomers (LTCFs). LTCFs were efficiently converted to the corresponding liquid terminated-hydroxyl fluoroelastomers (LTHFs) via a simple one-pot method. The reductive rate of LTHFs was analyzed by chemical titration. The structure of LTCFs and LTHFs was analyzed by Fourier transform infrared spectroscopy (FTIR), ¹H nuclear magnetic resonance (¹H NMR) spectroscopy and ¹⁹F nuclear magnetic resonance (¹⁹F NMR) spectrocopy. The results show that –C=C– and carboxyl groups of LTCFs are reduced efficiently. The effect of unitary metal hydride reduction systems and binary metal hydride reduction systems on the performances of the LTCFs reduction was compared. The results show binary metal hydride reduction systems are more efficient for reduction of LTCFs at ambient temperature. In addition, sodium borohydride/diisobutyl aluminum hydride binary metal hydride reduction system achieves the highest reductive rate (93%) and its reductive mechanism was investigated.

A novel bio-based multi-block copolyester, poly(2,5-tetrahydrofurandimethanol 2,5-furandicarboxylate)-multi-poly(1,3-propylene 2,5-furandicarboxylate) (PTPF), was synthesized by the melt interfacial co-polycondensation of poly(2,5-tetrahydrofurandimethanol 2,5-furandicarboxylate) (PTF) and poly(1,3-propylene 2,5-furandicarboxylate) (PPF). Owing to the partially alternating and partially random copolymer structure, PTPF showed thermoplastic properties intermediate between those of PTF and PPF, which was different from those of the corresponding PTF/PPF random copolymer. The chemical structures and properties of these copolyesters were investigated by ¹H NMR, ¹³C NMR, FTIR, DSC, TGA and torque rheometer. Similar solubility parameters between PTF and PPF were obtained by theoretical calculations, indicating the good compatibility between these two copolyesters. The T_g of PTF (75.2°C) was higher than that of PPF (56.1°C), suggesting the stronger rigidity of THFDM compared with 1,3-PDO. In addition, a significant shear thinning phenomenon was observed in the rheological test. Due to the unique thermal and rheological properties, PTPF may potentially be an alternative in the manufacture of fiber and film.